For example, a method of detecting a full charge capacity of a battery based on an integrated value of a charge and discharge current and a variation in a remaining capacity of a battery between first and second detection timings related to on and off of an ignition switch of a vehicle is disclosed in the related art (for example, refer to Patent Document 1).
In this method, the integrated value of the charge and discharge current is calculated by integrating a charge current and a discharge current of a battery. The charge current and the discharge current are detected by a current sensor between the first and second detection timings. In addition, when computing the variation in the remaining capacity, first, an open voltage of the battery is detected by a voltage sensor, for example, at each detection timing at which the charge and discharge current of the battery becomes zero. In addition, a remaining capacity corresponding to the open voltage of the battery is detected from a correspondence relationship between the open voltage, which is set in advance, of the battery and the remaining capacity. In addition, the variation in the remaining capacity is calculated from the remaining capacity at the first and second detection timings.